Suspected it was the thermostat, since temperature stayed the same at multiple settings over a 24 hr period. There was only three components inside the freezer besides the evaporator, the fan was working, so I decided to just go ahead and replace the thermostat and defrost thermostat. Also replaced the defrost timer by the compressor, just to get all the old parts replaced with new. I had already replaced the compressor, so now I've pretty much have a new freezer. The new parts works great and the freezer now shuts down as it should. Only took me about half an hour to install the parts with just screwdriver.